This invention relates to a broadband low-power nonlinear optics medium and, more particularly, to a nonlinear optics medium that may be used to generate a strong optical grating.
It is now well known that substantial radiation pressure forces can be exerted on small transparent dielectric particles by a laser beam. See, for example, the articles by A. Ashkin entitled "Acceleration and Trapping of Particles by Radiation Pressure," Physical Review Letters, Vol. 24, No. 4, Jan. 26, 1970, pp. 156-159 and "Applications of Laser Radiation Pressure," Science, Vol. 210, page 1081, Dec. 5, 1980. In the Ashkin articles a focused beam from a laser is used to trap small transparent spheres. Recently it has been proposed to use an aerosol of dielectric spheres to achieve a nonlinear optical medium. See the article entitled "Nonlinear Optics In Aerosols," by A. Jay Palmer, Optics Letters, Vol 5, No. 2, February 1980, pp. 54-55. Experiments are described in the Palmer article wherein an aerosol of dielectric spheres is utilized to provide a medium having a degenerate third order nonlinear susceptibility of the type that is required in four-wave mixing experiments. The particles proposed by Palmer had diameters in the order of 5 micrometers and, therefore, it was said that these particles would be restricted to spatial gratings having periods greater than about 50 micrometers. One difficulty encountered by Palmer is the fact that the particles of the aerosol tended to settle out in the presence of earth's gravity. Two methods were proposed to overcome this difficulty. The first method involved the suspension of the aerosol in an upward-directed flow field of a viscous medium, more specifically, in the presence of an upward-directed flow of air. The second method Palmer proposed was the levitation of the aerosol particles by electrostatically charging the particles and applying a vertical DC electric field as in the Millikan oil drop experiment. Both methods were found to be essentially unsatisfactory and Palmer concluded that the use of an aerosol as a nonlinear optic medium is most easily accomplished in the absence of gravity.